Solr drops/deletes all old documents while reindexing

Problem statement:

1. Solr delete/drops all the old documents when we click on the full-import od Data import handler. After the full import is complete, every thing works fine.

2. help me understand the JVM values attached as image, I am trying to connect it to the issue.

As per my understanding solr will not delete/drop the old documents till the new documents are imported fully. But in my case it drops the old documents while new documents are partially imported.

Details:

1. We are using Solr Cloud with single shard and 2 replica. S1-R1--------S1-R2
2. Using a amazon load balancer to balance the hit on each of them.
3. Both of the solr are attached to 3 zookepers.

4. Memory allocation: JAVA_OPTS="$JAVA_OPTS -Xms8192m -Xmx12288m -XX:PermSize=3072m -XX:MaxPermSize=8192m -Xss4m"

5. The solr admin panel is showing:

   • Physical Memory 98.2%
   • Swap Space 0.0%
   • File Descriptor Count 0.2%
   • JVM-Memory 34.3%